Thursday, 10 April 2014

IQ, Neuroticism, booze, and those damn vegetables again

A long suffering toiler in the groves of academe writes in to say that, rather than just bemoaning the lack of intelligence and personality measures in epidemiology, I should pay some attention to a study which has done precisely that, and help boost the visibility of such work in the health literature. In fact, I have a vague recollection of the paper, but now is the time to make amends for my forgetfulness.

Bryan Pesta apologizes for the “ghastly” link below, but it is free, folks, so just copy and paste into the search bar.

By way of background, to the external world the USA is a monolith with some minor regional variations. To its citizens is a union of sovereign states, and all the better for it when that union is not too close. Pesta, Bertsch,McDaniel, Mahoney and Poznanski (Intelligence 40 (2012) 107–114) have gathered data on all 50 American states, have found a link between IQ and neuroticism measures and health variables, and have tried to tease out possible causal links.

They found that at the State level, drinking alcohol correlates positively with exercising and eating fruits and vegetables; and it correlates negatively with rates of smoking and many chronic diseases. These data are consistent with a growing but mixed literature showing that alcohol consumption correlates inversely with chronic disease rates. This may be nothing to do with ethanol as such, but we should follow the tradition of results first, explanations later.

The authors work through the key data using multiple regression.

At Step 1, the linear combination of IQ and N alone explained 57% and 61% of the variance in Chronic Disease and Metabolic Syndrome, respectively. Both IQ and N remained significant (but attenuated) predictors of disease, after entering Health Behaviors at Step 2. Not surprisingly, Health Behaviors itself explained large amounts of variance (over IQ and N) in both Chronic Disease and Metabolic Syndrome. Note that the variance explained at Step 2 is unusually large for social science research. Fully 80% of the variance in Chronic Disease (77% in Metabolic Syndrome) was explained by the combination of IQ, N and Health Behaviors.The size of the effects here, though, could exemplify the "high resolution" that aggregate-level data offer, relative to studies that use individuals. At Step 3 they found that IQ (Beta=−.18), N (Beta=.35) and Health Behaviors (Beta=−.53) all remained significant as predictors of chronic disease, even after controlling for state income (Beta=−.12, ns).

Here are the correlations between IQ and :

Neuroticism−.08

Health Behaviours .45

Chronic disease −.51

Metabolic syndrome −.53 C

Crime −.76

Education .41

Religiosity −.55

Income .57

So, here we have a nice clean study, admittedly at State level (aggregated data) which shows the importance of IQ and Neuroticism in influencing health outcomes. Why has this engaging study only been cited once? It may be that the intelligence literature is not read by epidemiologists. Another problem may be the title: “Differential epidemiology: IQ, neuroticism, and chronic disease by the 50 U.S. states”. It is accurate but dull, and hardly worth tweeting about in its current form. I think that the Pesta gang need to get with the spirit of the age, and re-issue it with a snappier, media friendly title:

Dull worriers die sooner: Avoid West Virginia.

Disclaimer: I am sure that the denizens of West Virginia are bright and stable people. It was just a suggestion.

13 comments:

Before we get too excited about this paper, does it disaggregate the findings by race?

Second, even if you did that, as my post makes clear, ethnic differences within race, particularly Whites, makes it hard to make a straightforward comparison. You may find IQ confounded by ethnicity, although one would imagine IQ would predict longevity between groups as well as within groups (although, as we see in Europe, not necessarily – lower IQ SW Europeans live longer than higher IQ NE Europeans).

Albion's Seed. Pattern of original migration. Disaggregate by race and nation of origin. Agree to all that, but in fact none of that matters, because whatever the reason for having a particular IQ the interest is that it leads to particular behaviours and health outcomes. Indeed, if it turns out that they have different racial and cultural origins, that strengthens the argument that IQ is important.

Oh to be sure, IQ is predictive of health between groups. But a few key outliers jump out (Hispanics, at least in the US, SW Europeans, NE Europeans - although globally they're not such huge outliers) that complicate any attempt to try to craft a neat and simple explanation as to why the relationship exists. Those outliers also, fortunately, serve to call into question the importance of behaviors to outcomes... ;)

This may sound weird, but I think researchers often over-control for things when using regression. I call it regression soup: Whichever variable is “still significant” must be the cause / whichever variable is no longer significant (after control) cannot be the cause.

For example, it’s common to see IQ predicting something while controlling for education. This bothers me unless the authors at least also report the steps where IQ and education appear alone in the equations. Even still, given that IQ and education probably partly determine each other, how do we interpret any of this?

With regard to causality at the state-level, we envision a nexus of inter-correlated and co-causal variables (inspired by Jensen’s g Nexus). If true, regression or any of its variants does not seem powerful enough to get at causality.

I re-ran the original regression reported above and controlled for race. The multiple R predicting chronic disease was .90. Here are the Betas:

Coal mining in West Virginia was a huge business but now it requires few workers, so the people left behind tend to be the left behind-types. By the way, the nearby metropolis of Pittsburgh, the old steel capital, has economically stabilized on the back of its hospitals and medical centers, presumably treating in part the high level of chronic disease in West Virginia.

Dear Steve, Thanks for the update on West Virginia. From memory, Mississippi has poorer health outcomes and lower ability scores. Aggregated data certainly gives an interesting overview, though a representative and well followed birth cohort is probably the best of all.

it's a prejudice of the lower classes in the us that good people drink little or not at all.

nh consumes more per person than any us state.

in class terms nh is the king of the states.

i read a study recently which found a significant difference in brain volume between heavy drinkers and teetotalers.

i also remember a psy d who didn't know the difference between statistically and practically significant. he recorded in his notes that i was talking nonsense...and that i was above average to high average in iq and that future psy ds should know this as most of their clients were very dull.

well that same study found that the difference in brain volume between heavy drinkers and non-drinkers was a whopping...1.5%. ;) (that's the diff between statistical and practical significance, if you didn't get it.)

and i'm in the bgi study. i even told this psy d i'd made a perfect score on the gre general. he made no connection between such tests and iq tests.